Predictors of outcome in pediatric submersion victims treated by Seattle and King County's prehospital emergency services were studied. Victims less than 20 years old were identified from hospital admissions and paramedic and medical examiners' reports. The proportion of fatal or severe outcomes in patients were compared with various risk factors. Of 135 patients, 45 died and 5 had severe neurologic impairment. A subset of 38 victims found in cardiopulmonary arrest had a 32% survival rate, with 67% of survivors unimpaired or only mildly impaired. The two risk factors that occurred most commonly in victims who died or were severely impaired were submersion duration greater than 9 minutes (28 patients) and cardiopulmonary resuscitation duration longer than 25 minutes (20 patients). Both factors were ascertained in the prehospital phase of care. Submersion duration was associated with a steadily increasing risk of severe or fatal outcomes: 10% risk (7/67) for 0 to 5 minutes, 56% risk (5/9) for 6 to 9 minutes, 88% risk (21/25) for 10 to 25 minutes, 100% risk (4/4) for greater than 25 minutes. None of 20 children receiving greater than 25 minutes of cardiopulmonary resuscitation escaped death or severe neurologic impairment. Our rates for saving all victims, particularly victims in cardiopulmonary arrest, are considerably higher than has been reported before the children. Prompt prehospital advanced cardiac life support is the most effective means of medical intervention for the pediatric submersion victim. Prehospital information provided the most valuable predictors of outcome.